Flavoxate hydrochloride is a drug which has long been used therapeutically to limit the symptoms of pollakiuria, particularly nocturia, and of urinary incontinence originating from various pathological situations such as prostatitis, urethritis, cystitis and the side effects of radiotherapy or surgical therapy of the urinary tract. It has also been found that flavoxate is effective in the treatment and diagnosis of erectile impotence.
The therapeutic dose is usually 600-800 mg/day in 3-4 administrations, although in some cases a dose of up to 1200 mg/day has been found more effective. The problem in administering flavoxate hydrochloride derives from the fact that its half life is such that the duration of its therapeutic activity is about 5-6 hours. The short half-life of flavoxate makes it impossible for a patient to ingest a dosage form containing a sufficient amount of the active material in one administration to provide a therapeutic effect while the patient is asleep overnight.
Thus, a formulation able to maintain the therapeutic effectiveness of the drug for a longer duration would reduce the frequency of administration, and thereby considerably improve the quality of life of the patient, especially considering that the therapy using flavoxate is typically long term and prolonged and is particularly directed towards patients of advanced age.
Among all the possible pharmaceutical forms in which flavoxate hydrochloride can be administered, tablets, capsules or pills are the most suitable because they ensure that the exact prescribed quantity of product is taken. In addition, for practical reasons, it is advantageous for the treatment with the drug to take the form of a single tablet or capsule that is administered the smallest possible number of times per day. For example, administration of one tablet per day providing an effective plasma concentration of drug for 24 hours would be ideal.
As far as it is known to the applicant, only Japanese patent application JP 63-154619 and European patent application EP 250374 have confronted the problem of administering flavoxate hydrochloride employing delayed-release formulations. However, even by applying the teachings of these two patent applications, it is not possible to prepare pharmaceutical formulations that can be administered in a single dosage form when the dosage of the active ingredient is very large. In fact, in such cases, the final product would be of such a large size as to be practically unusable.
There is therefore, a need for formulations which provide a large dosage of the active ingredient, and which provide the total requirement for effective treatment, but are of limited size to make ingestion practical.